1. Field of the Invention
This invention relates to an electrochromic optical switching device. More particularly, this invention relates to an optical switching device comprising an electrochromic electrode and a reversible polymerization counter electrode.
2. Description of the Related Art
Electrochromism comprises a reversible color change which occurs in certain materials by an applied electric field or current. Electrochromic films made from such materials may be typically used in structures such as eyeglasses, sunglasses, protective goggles, switchable mirrors and sun visors, automobile windows, architectural windows, aircraft windows, marine windows, spacecraft windows, calculators, computer display screens, large area information displays (such as in airports, railway stations, motorways, stock exchange boards), voltage indicators, computer memory elements, auto headlamp covers, and windows for watches. Such electrochromic films can also be used on opaque substrates including metallic or metal-like surfaces and in combination with solar cells.
Lampert in "Electrochromic Materials and Devices for Energy Efficient Windows", published in Solar Energy Materials 11 (1984), pp. 1-27, North-Holland, Amsterdam, surveys the use of a number of compounds which are capable of functioning as electrochromic materials and discusses their applicability in particular for use in the construction of optical shutters for windows.
In a chapter entitled "Chemical and Optical Studies of Electrochromic Hydrated Nickel Oxide Films and Devices", in "Large Area Chromogenics: Materials and Devices for Transmittance Control", authored by Lampert and Granqvist and published by Optical Engineering Press, Bellingham, WA, 1990, the use of hydrated nickel oxide in the construction of electrochromic devices is particularly discussed.
While the characteristics of such electrochromic devices are of interest in a number of applications, construction of such devices is somewhat complicated. The electrochromic material used in such a device forms one electrode of an electrochemical cell. In particular, where transparent electrochromic devices are being constructed, the counter electrode of the cell must, therefore, either be a colorless electrode or a matching electrochromic material, i.e., a second material which will also become transparent at the same charge/discharge level as the first electrode. Since one electrode functions as the cathode and the other as the anode, two different electrochromic materials must be utilized which will have such matching or complimentary characteristics, which is not an easy task.
The cost of the electrode materials utilized is also a factor which must be taken into account, as well as the chemical compatibility of the electrode materials to one another, and to other materials used in the cell such as electrolytes, separators, insulators, etc. The choice of electrode materials is further constricted by the need to choose electrode materials which will not form insoluble (nonreversible) compounds in the cell which would otherwise greatly shorten the life of the device, i.e., the number of charge/discharge cycles.
It would also be advantageous, from the standpoint of handling, as well as corrosion, to use solid materials in preference to liquid materials in the construction of an electrochromic device.
Recently, the use of polymerizable organo-sulfur compounds as electrode materials for rechargeable electrochemical cells has been discovered. Dejonghe et al. U.S. Pat. No. 4,833,048 describes and claims such a cell wherein polymerizable organo-sulfur material serves as the cathode of such a cell. The polymerizable organo-sulfur material described therein has a general formula, in its charged state, of (R(S).sub.y).sub.n where y=1-6, n=2-20and R is one or more of the same or different aliphatic or aromatic organic moieties having 1-20 carbon atoms. When the organo-sulfur electrode material is in its charged state, the sulfur atom (or atoms) of the basic R-(S).sub.y -- group (monomer) forms an -S-S- bond with a sulfur atom of another R-(S).sub.y -- group forming, in its L simplest (dimerized) form, R-S-S-R, i.e., the polymerized state of the organo-sulfur electrode material.
Cells respectively utilizing liquid and solid versions of such organo-sulfur electrodes are further described and claimed in U.S. Pat. No. 4,917,974 and U.S. Pat. application Ser. No. 07/421,091, filed Oct. 13, 1989.